1. Field of the Invention
This invention relates to an electric power conversion device for variable-speed controlling of a motor driving a pump, for example and more specifically, to an electric power conversion device equipped with multiplex control units to enable it to continue controlling even if a control circuit breaks down in operation.
2. Description of the Related Art
For example, with respect to a power conversion device such as one used in a recirculation pump power equipment with variable frequency control in a nuclear power plant, generally only one control unit for controlling variable frequency is equipped with the power conversion device. That is, although a control device is composed as a single component, in an institution for which advanced reliability is required, such as a nuclear power plant, redundant dual components having both an operation system and a standby system as multiplex control units are adopted in consideration of safety.
Hereafter, a conventional example of the multiplex control units of the power conversion device is explained in reference to FIGS. 7 through 10. As shown in FIG. 7, a power conversion device 100 is connected between an AC power supply 1 and a motor 3 for driving a recirculation pump and is composed of a power converter 20 for variable-speed control of the motor 3.
As shown in FIG. 7, a conventional power conversion device has multiplex control units of a power converter 20, that is, it is composed of the power converter 20 as a control target, a control circuit A 121 and a control circuit B 122, which are arranged dual to control the power converter 20, a selector switch 21 for switching from one control circuit to another control circuit, and a selection circuit 22 for outputting a changeover selection signal to the selector switch 21. When the control circuit A 121 is operating, the control circuit B 122 is a standby. An input side circuit of the power converter 20 is connected to current transformers (CT) 101 and 102 for detecting circuit current, and an output side circuit of the power converter 20 is connected to power transformers 111 and 112, respectively. Detected outputs from the current transformer 101 and the power transformer 111 and detected outputs from the current transformer 102 and the power transformer 112 are inputted to the control circuit A 121 and the control circuit B 122, respectively.
As shown in FIG. 8A and FIG. 8B, in an ordinary state, the power converter 20 is controlled and driven by the control circuit A 121 as an operating unit (this is denoted as S41 in FIG. 8). When the power converter 20 works normally but the control circuit A 121 is broken for some reason (S42), the selection circuit 22 outputs a changeover selection signal to the selector switch 21, and the selector switch 21 changes a contact from the control circuit A 121 to the control circuit B 122 (S43), and the control circuit B 122, which was a standby equipment, starts to control the power converter 20 (S44), and continues the control of the power converter 20.
Moreover, as shown in FIG. 9A and FIG. 9B, in a case that the control circuit A 121 controls the power converter 20 (S51 in FIG. 9) and monitors a state of the power converter 20 by receiving detected signals of circuit and voltage from the current transformer 101 and the power transformer 111, respectively, etc., when the power converter 20 breaks down (S52), the control circuit A 121 detects an abnormal state of the power converter 20 (S53), the selector switch 21 receives a changeover selection signal outputted from the selection circuit 22 and switches a contact from the control circuit A 121 to the control circuit B 122 (S54). In this situation, if the control circuit B 122 also detects an abnormal state of the power converter 20, it judges this detection as a failure of the power converter 20 and stops operation of the power converter 20.
In the above-mentioned conventional multiplex control units of the power conversion device 2, when the control unit A 121 in an operation has broken (from S61 to S62 in FIG. 10), it is possible that the power converter 20 itself is influenced by the breakage of the control unit 121 and enters an abnormal state (S63).
In this case, while the power converter 20 has been in the abnormal state, even if the selector switch 21 changes a contact from the control circuit A 121 to the control circuit B 122 to try to continue the control of the power converter (S64), the control circuit B 122 also detects a failure of the power converter 20 (S65) since the power converter 20 is still in an abnormal state, and thus the power converter has to be stopped (S66) and here it becomes impossible to keep controlling of the power converter 20. Therefore, there is an issue concerning the reliability for a motion of the power control device 100. That is, though it may be equipped with multiplex control units, a breakdown of single a control circuit may make it impossible to continue controlling the power converter 20 and there is a possibility that the power conversion device 100 will stop operating.
In view of the foregoing, it is a main object of this invention is provide a power conversion device for addressing this issue with high reliability, equipped with multiplex control units for enabling continued operating and controlling of the power converter even if the single control unit breaks while preventing the power converter from being influenced by the breakdown.
Other and further objects of this invention will become apparent upon an understanding of the illustrative embodiments to be described herein or will be indicated in the appended claims while various advantages not referred to herein will be appeared to one skilled in the art upon employment of the invention in practice.
According to an aspect of the present invention, there is provided a power conversion device including, a power converter which controls a motor in variable speed control, a first control circuit which outputs a first control signal to control the power converter, a second control circuit which outputs a second control signal to control the power converter, a first detector which detects a state of the power converter and outputs a first detection signal to the first control circuit, a second detector which detects a state of the power converter and outputs a second detection signal to the second control circuit, a switch which receives the first control signal and the second control signal and outputs one of the first control signal and the second control signal to the power converter, a selection circuit which outputs a changeover selection signal to the switch for outputting the second control signal instead of the first control signal when the switch has outputted the first control signal and the first control circuit fails.
According to another aspect of the present invention, there is provided a power conversion device including, a power converter which controls a motor in variable speed control, a first control circuit which outputs a first control signal to control the power converter, a second control circuit which outputs a second control signal to control the power converter, a restore circuit which outputs a restoring signal to restore the power converter to return a previous state of the power converter, a first detector which detects a state of the power converter and outputs a first detection signal to the first control circuit, a second detector which detects a state of the power converter and outputs a second detection signal to the second control circuit, a switch which receives the first control signal, the second control signal and the restoring signal and outputs one of the first control signal, the second control signal and the restoring signal to the power converter, and a selection circuit which outputs a changeover selection signal to the switch, firstly for outputting the restoring signal instead of the first control signal, when the switch has outputted the first control signal and the first control circuit fails, and for outputting the second control signal instead of the restoring signal after the power converter has been returned to a previous normal state.
According to still another aspect of the present invention, there is provided a power conversion device including, a power converter which controls a motor in variable speed control, a first control circuit which outputs a first control signal to control the power converter, a second control circuit which outputs a second control signal to control the power converter, a third control circuit which outputs a third control signal to control the power converter, first, second and third detectors each of which detects a state of the power converter and outputs, respectively, first, second and third detection signals to, respectively, the first, second and third control circuits, and a majority selection circuit which receives the first, second and third control signals, determines which of these three control signals forms a majority and outputs one of such majority signals to the power converter.
According to still another aspect of the present invention, there is provided a control method of a power converter, which controls a motor in variable speed control, including, first detecting of at least one of a current and a voltage of a first circuit at a side of the power converter, second detecting of at least one of a current and a voltage of a second circuit at a side of the power converter, first generating of a first control signal to the power converter in a first controller corresponding to the first circuit, second generating of a second control signal to the power converter in a second controller corresponding to the second circuit, sending the first control signal to the power converter as a direct control signal, and after the sending of the first control signal switching the direct control signal to be sent to the power converter from the first control signal into the second control signal when failure of the first control circuit is detected.